Version May 2024
INTRODUCTION — Cardiopulmonary bypass (CPB) is a form of extracorporeal circulation in which the patient's blood is diverted from the heart and lungs and rerouted outside of the body. The right atrium (RA) or both superior and inferior vena cavae are cannulated to divert blood through the venous line of the CPB circuit, with return of the blood via an arterial cannula positioned in the ascending aorta or other major artery. Typically, the ascending aorta is cross-clamped and cardioplegia is administered to allow the cardiac surgeon to operate on a nonbeating heart in a field largely devoid of blood. The normal physiologic functions of the heart and lungs, including circulation of blood, oxygenation, and ventilation, are temporarily taken over by the CPB machine so that other end organs remain adequately oxygenated and perfused.
This topic will discuss preparations for and initiation of CPB. Management of CPB is discussed separately. (See "Management of cardiopulmonary bypass".)
The process of weaning from CPB and common problems encountered in the immediate postbypass period are addressed separately. (See "Weaning from cardiopulmonary bypass" and "Intraoperative problems after cardiopulmonary bypass".)
PREPARATIONS FOR CARDIOPULMONARY BYPASS — Prior to initiation of CPB, several key steps must be completed (table 1), including systemic anticoagulation and antifibrinolytic administration as explained in separate topics:
AORTIC, VENOUS, AND CORONARY SINUS CANNULATION — Key steps in preparing to initiate CPB include aortic and venous cannulation, as well as placement of a cannula into the coronary sinus for delivery of retrograde cardioplegia in selected patients. Typical positions of the vascular cannulae utilized during CPB are shown in the figure (figure 1).
Placement of the venous and coronary sinus cannulae requires surgical manipulation of the heart, which may cause hypotension, supraventricular arrhythmias, or blood loss. Hemodynamic instability usually resolves with administration of vasopressors and/or when the surgeon restores the heart to its normal position. Significant blood loss is treated by intravascular volume expansion through IV fluid administration or direct infusion of fluid from the CPB circuit into the arterial or venous cannula. Prompt initiation of CPB may be necessary to treat malignant arrhythmias or severe hypotension.
Aortic cannulation — Aortic cannulation is usually accomplished in the ascending aorta distal to the intended cross-clamp site but proximal to the takeoff of the innominate artery (figure 1) [1].
●Evaluation of the aorta before cannulation – Prior to cannulation for CPB, the ascending aorta is evaluated by surgical palpation and also typically with transesophageal echocardiography (TEE) to identify and avoid areas of atheromatous disease or calcification (image 1) [1-3]. Avoidance of surgical manipulation of aortic areas with known calcification or atherosclerotic plaque may reduce the risk of cerebral embolism and postoperative stroke [4-9], as well as the risk of acute kidney injury (AKI) [10-13]. Specialized aortic cannulae that incorporate embolic protection mechanisms are under investigation for use in the ascending aorta, but efficacy has not been established [14,15].
Many centers also perform epiaortic scanning of the ascending aorta prior to aortic cannulation and cross-clamping, either selectively or routinely, as a supplemental and possibly superior technique for identifying disease in the ascending aorta (image 1) [3,5,7,16,17]. This requires availability of a high-resolution (>7 MHz) ultrasound transducer, which is inserted into a sterile sheath filled with either sterile saline or ultrasound transmission gel before placement directly on the exposed ascending aorta for enhanced imaging of atheromas and calcification. These technologies provide guidance for the surgeon regarding selection of sites for aortic cannulation, and also for cardioplegia administration, aortic cross-clamping, or placement of the "side-biter" clamp to complete proximal anastomoses during CABG. (See "Management of special populations during cardiac surgery with cardiopulmonary bypass", section on 'Cerebrovascular disease'.)
In some cases, a less common site may be chosen for arterial cannulation such as the right axillary artery or right or left femoral artery. Examples include identified severe ascending aortic calcification and selected cases involving redo sternotomy, thoracic aortic procedures, or minimally invasive cardiac procedures. (See "Preoperative evaluation for anesthesia for cardiac surgery", section on 'Chest radiograph and computed tomography imaging' and "Anesthesia for aortic surgery with hypothermia and elective circulatory arrest in adult patients", section on 'Preparations for cardiopulmonary bypass'.)
The descending aorta is also examined using TEE. Atheromatous disease of the descending aorta predicts stroke and death after CABG since coexisting ascending aortic disease is likely; thus, extra caution is warranted during any manipulation of the aorta [18]. Furthermore, identification of severe atheromatous disease or mobile plaques in the descending aorta may affect decision-making for cannulating the femoral artery for CPB or insertion of an intraaortic balloon pump (IABP) into the femoral artery with retrograde passage through the diseased aorta (image 2). (See "Intraaortic balloon pump counterpulsation", section on 'Complications'.)
●Control of blood pressure – In preparation for cannulation, the surgeon typically requests that the systolic blood pressure be controlled within a range between 90 to 120 mmHg to minimize risk of vessel injury, aortic dissection, intramural hematoma, or uncontrolled bleeding during aortic instrumentation [19]. If an intra-aortic balloon pump (IABP) has been previously inserted, balloon inflation and deflation are temporarily paused during cannulation.
●De-airing and testing the aortic cannula – Once the aortic cannula is properly positioned and “de-aired,” the surgeon connects it to the arterial tubing of the CPB circuit. This arterial line is then "tested" by the perfusionist to confirm proper intraluminal placement. If using a roller pump, this is accomplished by initiating arterial flow to the patient and confirming that there is no unusual increase in arterial line pressure as flow is increased. If using a centrifugal pump, the perfusionist confirms that the expected flow is achieved with a set number of rotations per minute (RPM), while observing the patient's mean arterial pressure (MAP). If testing is uneventful, rapid administration of fluid from the CPB machine via this cannula is possible (eg, if needed to replace blood loss or correct hypovolemia before CPB is initiated).
Venous cannulation — After aortic cannulation, venous cannulation is most commonly performed through the appendage of the right atrium (RA), with the distal tip of the cannula positioned in the inferior vena cava (IVC), thereby allowing for drainage of both the IVC and the RA [1]. This so-called dual-stage or two-stage cannula provides excellent venous drainage with a single cannula since there are multiple holes near its tip in the IVC, as well as side holes located a few centimeters more proximally in the body of the RA (figure 1).
Alternatively, the superior vena cava (SVC) and the IVC can each be separately cannulated through the RA [1]. Such bicaval cannulation is used when it is necessary to enter the RA to perform the surgical procedure (eg, tricuspid valve operation) or if venous drainage would be compromised by distraction of the heart (eg, during surgical exposure for a mitral valve operation performed through the left atrium [LA]). When bicaval venous cannulation is used, medications that are administered during CPB such as vasopressors, anesthetics, or insulin should be administered by the perfusionist directly into the venous reservoir or into a catheter with a tip that exits into the superior vena cava. Intravenous drugs administered into a catheter with its tip in the right atrium may not achieve systemic distribution during CPB with bicaval venous cannulation with caval snares because the right atrium is excluded from the circulation.
Finally, femoral venous cannulation with a multiorifice catheter that is passed up the IVC into the RA/SVC is sometimes used for minimally invasive or redo procedures if access to the right atrium may be limited [20].
Coronary sinus cannulation — The surgeon may also place a cannula through the wall of the RA and into the coronary sinus before onset of CPB. This cannula will be used for delivery of retrograde cardioplegia during CPB. Although placement of the coronary sinus catheter is typically guided by surgical palpation, the anesthesiologist may assist by providing TEE imaging and confirmation of catheter tip position. Correct placement of the catheter may be further confirmed by measuring coronary sinus pressure and noting the presence of pulsatile coronary sinus pressure with the catheter balloon inflated. Coronary sinus pressure is measured by connecting to sterile tubing, which is then passed off the sterile field and connected by the anesthesiologist or perfusionist to a pressure transducer. For minimally invasive robotic surgical procedures, coronary sinus cannulation for cardioplegia may be achieved by the anesthesiologist through percutaneous right internal jugular venous cannulation with TEE guidance. (See "Minimally invasive aortic and mitral valve surgery", section on 'Access for cardiopulmonary bypass and cardioplegia'.)
INITIATION OF CARDIOPULMONARY BYPASS — After aortic and venous cannulation and confirmation of adequate systemic anticoagulation, the patient is ready for transition to CPB (figure 2). Several key steps are completed in rapid succession during initiation of CPB (table 1). We agree with professional society guidelines recommending use of an institution-specific checklist prior to initiating CPB [1].
Autologous priming — Significant hemodilution will occur at onset of CPB as the patient's blood volume intermixes with 1.0 to 1.5 L crystalloid CPB prime. Techniques such as retrograde autologous priming (RAP) and/or antegrade autologous priming (AAP) are typically used to limit hemodilution by replacing the circuit prime with the patient's blood, thereby reducing the crystalloid priming volume [1,21-29]. Either technique reduces crystalloid prime by approximately 400 to 800 mL. These techniques are a useful component of blood management in selected adults, particularly those with excessive intravascular volume [30]. (See "Blood management and anticoagulation for cardiopulmonary bypass", section on 'Strategies to minimize further hemodilution'.)
Specific techniques for autologous priming include the following:
●Retrograde autologous priming – RAP is typically performed over the course of two to five minutes as the perfusionist controls retrograde flow from the aortic cannula back into the CPB circuit to "retrograde" prime the circuit before initiating forward CPB flow. This retrograde flow displaces crystalloid prime into a separate bag that is connected to the arterial line (but is discontinuous from the pump circuit). Following RAP and when the surgeon is ready, venous drainage is engaged to initiate CPB and pump flow into the circuit, the oxygenator, and the arterial cannula. Vasopressors are typically administered during the RAP process to maintain mean arterial pressure (MAP) at 50 to 60 mmHg until full forward CPB flow has been established.
In a 2021 meta-analysis that included 11 randomized trials (1337 patients) and 10 observational studies (2327 patients), RAP was associated with reduced intraoperative red blood cell (RBC) transfusions (odds ratio [OR] 0.34; 95% CI 0.22-0.55; 18 studies), as well as reduced RBC transfusions during the entire hospitalization (OR 0.28; 95% CI 0.19-0.41; 5 studies) [28]. However, the volume of RAP is limited if hypovolemia or hypotension are present, and is not feasible due to safety concerns in some patients (eg, those with critical coronary or cardiac valve disease or cerebral comorbidities).
●Antegrade autologous priming – An alternative technique is antegrade autologous priming (AAP), which involves displacement of crystalloid priming volume as venous blood is continuously drained from the right atrium (RA) into the venous reservoir, and is then pumped into the circuit during initiation of CPB (while chasing the crystalloid prime into a separate bag connected to the arterial line). Since AAP occurs during the initiation of bypass, not prior to bypass like RAP, it does not subject the patient to a prebypass period of potential hypovolemia and hypotension. Consequently, it is more safely used as a routine method to decrease CPB circuit priming volume, and in patients with limitations or contraindications to RAP.
●Combined retrograde and antegrade autologous priming – Some institutions combine the autologous priming techniques described above.
Details by which autologous priming is accomplished vary significantly, depending on the bypass circuit design and local clinical preferences. However, the success of any autologous priming approach depends on reducing the volume of the circuit priming solution, which in turn depends on the patient's size and prebypass intravascular volume status. Pre-existing patient hypovolemia limits safe performance of these techniques. To avoid organ hypoperfusion, the anesthesiologist and perfusionist must recognize and treat hypovolemia during initiation of CPB and may need to abandon further efforts to complete autologous priming.
Discontinuation of ventilation — Ventilation of the lungs should be continued during initiation of bypass while the heart is still ejecting blood [31]. Once full CPB flow is achieved and evidenced by lack of pulsations noted on the systemic arterial (and pulmonary artery) pressure monitoring lines, lung ventilation is discontinued because apnea optimizes surgical conditions by creating a still surgical field. Fresh gas flow administered via the anesthesia machine is reduced to a minimum.
Ventilation of the lungs during CPB has not been demonstrated to improve pulmonary function following surgery [32,33]. A systematic review of 15 randomized controlled trials showed that compared with apnea, use of continuous positive airway pressure during CPB improved postoperative alveolar-arterial oxygen gradient differences, but did not shorten postoperative ventilation or hospital stay [32-34]. However, whenever the cardiac operation is performed with the use of only partial CPB (ie, if the pulmonary circulation is not entirely bypassed), lung ventilation remains necessary to oxygenate the pulmonary blood flow.
Discontinuation of cardiac support — If inotropic agents were administered prior to CPB, these agents are typically discontinued during CPB to reduce myocardial oxygen consumption. Vasopressor agents may need to be administered or continued if MAP is low. (See "Management of cardiopulmonary bypass", section on 'Mean arterial pressure'.)
If an intra-aortic balloon pump (IABP) is in place and functioning, IABP counterpulsation is typically discontinued upon initiation of CPB and for its duration. Although the IABP has been used to produce arterial blood pressure pulsatility during CPB, studies have not demonstrated improved outcomes with this technique. Furthermore, inflation of the balloon within the descending thoracic aorta may obstruct blood flow delivered via the aortic cannula [35,36].
Administration of anesthetic agents — Administration of volatile inhalation agents via the anesthesia machine is discontinued when CPB is initiated and is typically replaced simultaneously by administration of a volatile anesthetic via a vaporizer located in the gas line of the CPB circuit (in series with the air/oxygen blender for the oxygenator) [1,37]. During CPB, general anesthesia is typically maintained with a volatile anesthetic inhalation agent. Use of a total intravenous anesthetic (TIVA) technique during cardiac surgery, or combinations of volatile and intravenous agents are reasonable alternatives, as discussed in a separate topic. (See "Anesthesia for cardiac surgery: General principles", section on 'Maintenance techniques'.)
Aortic cross-clamping and antegrade cardioplegia administration — Prior to aortic cross-clamping, an antegrade cardioplegia cannula is inserted into the proximal ascending aorta (figure 1). During periods when cardioplegia is not being administered, this cannula serves as an aortic root vent to maintain a decompressed left ventricle (LV) during CPB. Just before placement of the aortic cross-clamp, the surgeon asks the perfusionist to reduce pump flow rate transiently so that MAP is reduced during clamp placement. After the aortic cross-clamp is placed, antegrade cardioplegia is administered to achieve cardiac arrest and myocardial protection [38]. The electrocardiogram (ECG) is monitored to ensure complete cardiac arrest (ie, absence of myocardial electrical activity). Aortic root images obtained with transesophageal echocardiography (TEE) and continuous pulmonary artery pressure (PAP) are monitored for evidence of ineffective delivery of antegrade cardioplegia (eg, in a patient with aortic regurgitation [AR]). (See "Management of special populations during cardiac surgery with cardiopulmonary bypass", section on 'Provision of adequate cardioplegia'.)
Standard hypothermic and hyperkalemic cardioplegia solutions are subsequently administered, typically in a ratio of 4:1 (4 parts blood to 1 part crystalloid), at regular intervals to maintain cardiac arrest. Alternatively, the del Nido formula may be administered in a ratio of 1:4 (1 part blood to 4 parts crystalloid) as a single-dose cardioplegia solution [39-41]. Less commonly used than a blood cardioplegia solution, pure crystalloid cardioplegia may be selected in some instances (eg, patients with cold agglutinins) [42,43].
Retrograde cardioplegia administration — In addition to anterograde cardioplegia, it may be necessary or desirable for convenience to subsequently administer retrograde cardioplegia solution into the coronary sinus to achieve and maintain complete cardiac arrest and myocardial preservation. Examples include aortic root replacement with coronary reimplantation, patients with multiple coronary stenoses with potentially poor preservation of distal myocardium if only antegrade cardioplegia is employed, and those with moderate or severe AR. (See "Management of special populations during cardiac surgery with cardiopulmonary bypass", section on 'Provision of adequate cardioplegia'.)
During delivery of retrograde cardioplegia, coronary sinus pressure is continuously measured. (See 'Coronary sinus cannulation' above.). The target maximum pressure is typically 40 mmHg
Other myocardial protection techniques — In some institutions, an infusion of glucose-insulin-potassium (GIK; eg, 50 mL of 40% glucose containing 1 unit of insulin per gram of glucose as well as 10 mEq of potassium chloride) is administered slowly via a central venous catheter to enhance the myocardial protective effects of cardioplegia and attenuate LV dysfunction after CPB [44,45] (see "Intraoperative problems after cardiopulmonary bypass", section on 'Left ventricular dysfunction'). In one randomized trial, slow administration of 50 mL GIK solution over 60 minutes after anesthetic induction to 110 patients was compared with administration of 50 mL saline placebo to 112 patients [44]. Pretreatment with GIK solution resulted in less LV dysfunction (defined as new or worsening LV dysfunction requiring inotropic support for more than 120 minutes after CPB; risk ratio [RR] 0.41, 95% CI 0.25-0.66), as well as lower troponin levels on the first postoperative day (2.9 ng/mL, interquartile range [IQR] 1.5-6.6 versus 4.3 ng/mL, IQR 2.4-8.2).
Left ventricular vent placement — An LV vent is typically employed in left-sided intracardiac procedures (eg, aortic or mitral valve repair or replacement) because blood filling the LV from the pulmonary vasculature or Thebesian veins obscures the surgical field. Furthermore, an LV vent prevents LV distention, and is used to assist with removal of air from the left heart chambers in preparation for weaning from bypass.
The surgeon introduces the LV vent via the right upper pulmonary vein, then advances it through the mitral valve and into the LV (figure 1). Correct placement of the vent and effective decompression of the LV may be confirmed with TEE examination.
Placement of an LV vent may occasionally be necessary to avoid or treat LV distention, which, if persistent, may result in severe postbypass LV dysfunction. For example, if AR is present during antegrade delivery of cardioplegia (figure 1), LV distention will occur. Although prebypass TEE assessment of the aortic valve typically allows anticipation of this problem and planning for administration of retrograde cardioplegia (see "Management of special populations during cardiac surgery with cardiopulmonary bypass", section on 'Left ventricular distension'), unanticipated LV distention during cardioplegia infusion occasionally occurs. This is easily recognized visually by the surgeon, who can halt administration of antegrade cardioplegia and insert an LV vent to decompress the LV. LV distention may also be noted by the anesthesiologist on TEE images or as a large increase in PAP occurring due to backflow of intraventricular volume into the left atrium and pulmonary venous system (image 3). Then, the remainder of the antegrade cardioplegia can be given or retrograde cardioplegia can be initiated.
FURTHER MANAGEMENT OF CARDIOPULMONARY BYPASS — After initiation of CPB, ongoing management is necessary, as discussed separately. (See "Management of cardiopulmonary bypass".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Management of cardiopulmonary bypass".)
SUMMARY AND RECOMMENDATIONS
●Key preparation steps – Key steps in preparation for cardiopulmonary bypass (CPB) are systemic anticoagulation, antifibrinolytic administration, aortic cannulation, and venous cannulation (table 1 and figure 2 and figure 1). (See 'Preparations for cardiopulmonary bypass' above and 'Aortic, venous, and coronary sinus cannulation' above.)
●Aortic cannulation – Aortic cannulation is typically accomplished in the ascending aorta distal to the intended cross-clamp site but proximal to the takeoff of the innominate artery. Sites for initial aortic cannulation and later cross-clamping can be guided by transesophageal echocardiography (TEE) and by epiaortic echocardiography in selected cases (image 1), in order to decrease risk of atherosclerotic or calcific emboli that may cause stroke or acute kidney injury (AKI). (See 'Aortic cannulation' above and 'Aortic cross-clamping and antegrade cardioplegia administration' above.)
●Venous cannulation – Venous cannulation is performed through the appendage of the right atrium (RA), with the distal tip of the cannula positioned in the inferior vena cava (IVC), thereby allowing for drainage of both the IVC and the RA. (See 'Venous cannulation' above.)
●Autologous priming – We suggest an autologous priming technique to limit hemodilution by replacing the circuit prime with the patient's own blood for most adults undergoing cardiopulmonary bypass (Grade 2C). Although not feasible due to safety concerns in some patients (eg, those with critical coronary or cardiac valve disease, cerebral comorbidities, or significant hypovolemia or hypotension), this technique is a useful component of blood management in selected adults, particularly those with excessive intravascular volume. (See 'Autologous priming' above.)
●Discontinuation of ventilation – Once full CPB flow is achieved and cardiac ejection has ceased, lung ventilation is discontinued because apnea optimizes surgical conditions by creating a still surgical field. Fresh gas flow administered via the anesthesia machine is reduced to 0.5 L/minute. (See 'Discontinuation of ventilation' above.)
●Administration of anesthetic agents – Administration of inhalation anesthetics via the anesthesia machine is discontinued when CPB is initiated, and is simultaneously replaced by administration of a volatile anesthetic via a vaporizer located in the gas line of the CPB circuit. Use of a total intravenous anesthetic (TIVA) technique during cardiac surgery, or combinations of volatile and intravenous agents are reasonable alternatives. (See 'Administration of anesthetic agents' above.)
●Antegrade cardioplegia – When antegrade cardioplegia is administered after placement of the aortic cross-clamp, the electrocardiogram (ECG) is monitored to ensure absence of cardiac electrical activity indicating complete cardiac arrest. The TEE and pulmonary artery pressure (PAP), if available, are monitored for evidence of aortic regurgitation (AR) or left ventricular (LV) distention. (See 'Aortic cross-clamping and antegrade cardioplegia administration' above.)
●Retrograde cardioplegia – When retrograde cardioplegia is to be administered into the coronary sinus, TEE guidance can be used to verify correct catheter placement. Coronary sinus pressure is monitored during delivery of retrograde cardioplegia by connecting the catheter to sterile tubing leading to a pressure transducer. (See 'Coronary sinus cannulation' above and 'Retrograde cardioplegia administration' above.)
●Left ventricular venting – If LV venting is necessary to avoid or treat LV distention (eg, due to AR), correct vent placement and effective decompression are confirmed with TEE. (See 'Left ventricular vent placement' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Ryan Konoske, MD, who contributed to an earlier version of this topic review.
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